Railway signaling systems



June 7, 1960 w. Y. SPEIGHT RAILWAY SIGNALING SYSTEMS 2 Sheets-Sheet 1 Filed 001.. 28. 1957 V INVENTOR. Plbsleg K .Sjrezylz. BY 10,4 ,W

l l J 111.; ammonzvrr June 7, 1960 w. Y. SPEIGHT RAILWAY SIGNALING sys'raus 2 Sheets-Sheet 2 Filtd Oct. 25, 1957 United StatesPatent RAILWAY SIGNALING SYSTEMS Wesley Y. Speight, Bcllaire, Tex., assign'or to Westinghouse Air Brake Company, Wilmerdjng, Pa., a comeration of Pennsylvania Filed Oct. 28, 1957, Ser. No. 692,927

8 Claims. (Cl. 246-e-34) My invention relates to a railway signaling system. More particularly, my invention relates to a coded track signaling system using master and feedback codes to control the wayside signals governing train movements in opposite directions through a stretch of single track railway.

Coded track signaling systems using master and feedback codes, also termed normal and reverse codes, respectively, are well known in railway signaling art. They have been used frequently for signaling systems for single track railways of the form known as Absolute Permissive Block signaling (hereinafter designated APB.) and have also been used to provide additional controls through the reverse code for such functions as approach lighting of signals, additional block indications, and switch control. Considering herein only those coded track systems using a frequency code for the master or normal coded track current, such systems use a plurality of code rates to provide a plurality of indications in the direction governed by the master code. The reverse code heretofore has generally been limited to a polar code with two active indications, that is, two types of code pulses, and one indication obtained through the no-code condition. Even though the normal code may have a plurality of rates, this limitation for the reverse code still exists since such reverse codes must be independent of the normal codes as to the indications which they carry. That is, although'the reverse code is generated as a result of the reception of the normal' code through the track rails, the indication transmitted by the reverse code at any particular time must be independent of the indication being transmitted at the same time by the normal code in accordance with the code rate used. It is understood, of course, that the code rate of the reverse code is always identical with that of its master driving code.

The provision of additional indications carried by the reverse code is an advantage in A.P.B. signal systems and also in systems for approach lighting and other functions. In A.P.B. signaling, additional indications carried by the reverse code provide for overlap of signal controls at the station locations. been frequently necessary to reverse the direction of flow of the normal and reverse codes from one track section to another in the single track stretch in order to obtain the desired overlap throughout the station areas for additional safety in the system. With an additional indication possible in the reverse code, it will not be necessary to reverse the code direction from one track section to another. In other words, the reverse code may carry the overlap controls for the'traflic direc-' tion in which it governs in a manner similar to the carrying of such controls by the normal code. With an additional indication available in the reverse code direction, the approach lighting of signals section by section is possible in such A.P.B. systems rather than from station to station. However, it is apparent to those skilled in the art that additional indications in the reverse code Heretofore, it has relay responsive to the normal code pulses.

2,939,948 Patented June 7,

2 are possible only through combinations of the two available polarities. In other words, each additional indication comes only by providing an active indication comprising some combination of positive and negative polarity pulses. 1

Accordingly, an object of my invention is to provide a coded track signaling system using normal and reverse codes and having an additional indication in the reverse code direction.

A further object of my invention is to provide a coded track signaling system having at least three indications in both the master and feedback code directions.

Another object of my invention is to provide an APB. signaling system using normal and reverse track codes with each type code having sufficient active indications to carry all the required controls for governing traffic movement in one direction of travel. 7

It is also an object of my invention to provide, in a coded track signaling system, a reverse code generator capable of supplying three independent, active indications.

Still another object of my invention is to provide a reverse code generator for coded track signaling systems which is capable of transmitting a polarized reverse code at times having a combination of the available polarities of track current Other objects and features of my invention will become apparent from the following specification when taken in connection with the accompanying drawings.

In signal systems embodying my invention, there is pro vided, for each track section, a master or normal coded track circuit carrying three frequencies or code rates for control of the wayside signals. This master code is transmitted from the same end of each track section and controls the signal governing train movements entering at the opposite end of the section. These normal code pulses are received at the other end of the section by a track relay which drives the decoding circuit arrangement and the reverse code generator. The reverse code generator includes, in a first form of the apparatus, a double armature relay as the reverse code transmitter relay and a pair of stepping relays to at times selectively pole change the connections to the transmitter relay. In a second form of the apparatus, two reverse code transmitter relays are selected by a pole changing relay, the entire arrangement being driven by the track In either form, the operation of the reverse code generator means results in the transmission of reverse code pulses at times having a single polarity and at other times having alternately opposite polarities, that is, positive and negative pulses. These reverse code pulses are transmitted in the usual manner, one during each off-period of the normal code.

The normal frequency code is decoded by a mechanically tuned circuit arrangement. The two higher code speeds control the clear and approach indications of the associated signal governing entrance of trains into the section. The lowest code speed is used only as a carrier for the reverse code, the signal governing movements in the normal code direction being controlled to its stop indication during this period. The polar reverse code is decoded at the opposite end of the section, that is, the end from which the normal code originates, using relay type decoding. The relay circuit arrangement includes a decoding relay for each polarity and a third relay to detect any code following operation of the track relay. The decoding of a combination of polarities received by the track relay results in the display of a clear indication by the associated entering signal. Pulses of a single polarity, which may be selected as the positive polarity, result in an approach indication while pulses of the aforementioned dotted line.

V the other polarity alone result in a stop indication and are used to control overlap or approach lighting. 7 Referring now to the drawings, Fig. 1 shows, diagrammatically, apparatus embodying a first form of my inven-' tion used in a signal systemfor a Singlesectionof single refer to similar parts of the apparatus.

In the drawings, conventional symbols commonly used in the art havebeen used wherever possiblein order to .simplifyflthe showings for aneasier understanding. For .eXampIe'QSIQw-acting' relays are so designated by vertical arrows drawn through the movable portion of the relay contacts, the arrow pointing up or down to indicate the direction in which the relay is slow acting. Biased'relays are designated by arrows shown within the winding sym- 7 1:01 forthat relay. Such relays are characterized by the operation ofrelay armatures to close front contacts only when the energizing current flows through the relay winding in the directionof the arrow. Flow of current in the opposite direction, as well as deenergization of the relay winding, results in the releaseof the relay armature closing back contacts. Magnetic stick relays are also deignated by an arrow shown within the symboifor the relay winding, but these relays'are distinguished from "the biased type by also showing the movable' portion of the relay contacts in the vcrticalposition. When current flow through the relay winding (either winding in two winding relays) is in the direction of the arrow, these contacts are operated tothe left-hand or normal position. Flow of current through either or both windings of such relays 'in a direction opposite to the arrow results ,in the closing of right-hand or reverse contacts. These relays have a further characteristic of holding the contacts in the position to which they were last operated when the relay winding or windings are deenergized. A' further conventional symbol is the showing of contacts of code following. relays in a dotted manner in both the energized and released positions. Such showing indicates that the a movable portion of the contact is continuously. following a' coded current, at least in the condition shown inthe drawings, so that it alternately closes front and back contacts. Where such a code'following contact normally ioccu'pics one, or the. other position and-only at times follows code, the normally occupied positionis shown by a solid line with the code following position indicated by The rails of the track section are shown by the conventional single line symbol commonly used. The track circuit connections to the rails must thus more shown conventionally by a dotted line and bracket joining the two leads from the track circuit arrangement atfeach location. To assist in the understanding of the circuits traced, (+).and symbolsare shown adjacent the ,leads at each end of the track section to indicate those track leads which are connected tothe same rail.- The wayside signals in the track diagramare shown by conventionalisernaphor'e symbols with a heavy line indicating the position which the signal usually occupies, herein ;the' vertical or clear position. It is'to be understood, of course, that the actual wayside signals may be of any type ,well known in the art, for example, color light, search jlight, orposition light signals. Such showing as is necessaw in the circuit arrangement'of the drawingsis in the 'form of -colorlightfsignals having three lamps, green,

yellow; andred, respectively designated G, Y, and R.

Each set of lamps shown is connected to the corresponding trackside symbol .by a dotted line. Finally, each 10- .cationis provided with a local source of direct current :energy which maybe a battery of proper size and capacigovern traffic out-of and into the section.

one for each direction of t'rafi'ic movement.-

location.

fteryzf-I'B. I I H v Relay 3RC a biased relayhaving two separate and T 1 'ty. However, for simplicity, e source of energy as such is not shown and onlyits'positive and'n'egative terminals are indicated by the usual reference characters B and N, respectively. Y i 7 Referring now to -Fig. 1, there is shown across the top of this drawing a conventional track diagram of a single tracksection which extends between a double signal'location at the left or west end and'a similar double signal location at the right or east "end. The siectiom'designated 23T, is setoff fromltheremain'der ofjthe'stretch by irisulated joints,.shown conventionally by heavy bars drawn perpendicular to the single line track symbol; 'As previously indicated, this one section maybe considered as part of a single track stretchbetweenstations which is provided with a A;P.B. signaling system. At the west end of section 2-3T, signals 16 and 2G, respectively, At the east end, signalsSG andAG, respectively, govern traffic into and out-of the same section. Stated in other words, signals 1G andSG govern westbound train movements into and out-of section 2-3T, while signals 2G and 4G. govern :eastbound trainmovements into ancient-of the section.

As will appear hereinafter, the apparatus shown controls directly only signals 26 and 3G,the opposing entering signals for this track section. a Y

Section 2-3T is provided with-two coded track circuits, Each track circuit controls the entering signal atithe end of the section at which the-code pulses arereceived. Each track circuit is supplied withenergy froina track battery generally designated by the reference character TB, with a prefix corresponding to the entering signal at that location. Each section is further provided. with a track relay generally designated .by the reference character TR again plus a prefix corresponding to the entering signal at that Thus, at [the west end, there is locatedtrack battery 2TB and track relay ZTR and at the eastend track battery 3TB and-track relay 3TR. The master or normal coded track circuitmay be traced from the positive terminal of batteryi TB overnormal contact a of 'code transmitter-repeater relay- ZCTP, one rail' of' the track sectiomback contact in: of reverse code transmitter .relay 3RC, the winding of relay 3TR in the, direction of the arrow, backcontact of of relay 3RC,- and the other rail of the track 'section tothe negative terminal of batdistinct armaturestructures,.termed the: normal and the reverse armatures, each of which is provided with an associated set of contacts whose operation'is'se parate from that of the otherset offcontactsa Each armature is responsive to'current flowing through the singlerelay winding in one direction only, operating to :close associated 'front; contacts only under this conditionq A-t all other times, the armatures are biased to close associated back i'contactsQas' in any biased -relay. The normal armature of relay 3RC is responsive to current flowing through the winding in thedirection ofth e .left-hand'arrow, designated n, within the relay winding symbol. V The reverse armature is responsive to current flow in the oposite direction as indicatedbythesecond' arrow designated'r. The contactsassociate d withthe normal'armature are designated bya suilix adde d to the conventional letter reference for the contact,-while the contacts associated with the reverse arrnature are identified by the suffix 1' added to the otherwise conventional letter reference for the contact.= As these contacts are referred to hereinafter,. the use of these suflixes wilLserve to distinguish betweentheltwo sets of contacts. Track relaylTR 10- cated at the west; end, ofthe section is a similar type relay and its ;contacts-associated with'ithe left and right armaturesare likewise distinguished by the use of similar sufiixes'added rto the conventional letterreference char acters for the contacts. lt is to beunderstood that either of these-double armature biased relays may bereplaced while the second relay is responsive to current flowing in the opposite direction.

The reverse code track circuit may be traced from the positive terminal of track battery 31 B over front contact an of relay 3RC, one rail of the track circuit, reverse contact a of relay ZCTP, the winding of relay 2TR, the other rail of. the track section, and front contact In: of relay 3RC to the negative terminal of battery 3TB. In the. circuit just traced, it is evident that the positive terminal of the track battery is connected to the rails through the lead designated by the symbol At the other times in the operation of the reverse code circuit, front contacts ar and br of. relay 3R0 replace, respectively, front contacts an and bn. It is obvious from an inspection or the drawings that, in this condition, the positive terminal of the track battery is connected to the rails over the track lead designated by the symbol so that the polarity of the reverse code pulses is pole changed when the connections are made in this second manner.

The apparatus shown in Fig. l at the west end of the track section is not actually a part of my invention, but necessary for cooperation with the circuits of my invention in order to provide a complete signaling system of the ALPB. type. The circuit arrangement at the west end or" the section is disclosed in the copending application for Letters Patent, of the United States, Serial No. 692,926, filed on the same date as this application by C. W. Failor and C. E. Staples for a Railway Signaling System, the two applications having the same assignee. I shall describe briefly the operation of the circuits at the. west end and, in more detail, the cooperation between these circuits and the circuits at the east end embodying my invention. Reference, is made to the copending Failor and Staples application for a disclosure of a complete A.P.B. signaling system in which the circuits of my invention may be used.

As part of the apparatus at the west end of'the section, three code transmitters are provided which serve to establish code rates for the master track code. Each of these transmitters is designated by the reference character CT with a numerical prefix which indicates the code rate in code pulses per minute at which the corresponding transmitter operates. For example, code transmitter 180CT operates at the code rate of 180 pulses per minute. so that it alternately closes its front and back contacts at this code frequency. Any well known type of code transmitter may be used, but for purposes of this description they are shown and will be considered as being of the relay type which is particularly well known in the art. Each of the code transmitters is permanently energized, their windings being connected directly between terminals B and N of the local source. Thus, each transmitter alternately closes its front and back contacts at the code'rate designated by the numerical prefix associated with that transmitter.

The actual transmission of the master code pulses into the rails of the track section is controlled by the code transmitter repeater relay ZCTP. Relay ZCTP is of the magnetic stick type so that its contacts will remain in the normal or reverse position to which they were last operated if the relay winding is deenergized; One circuit for energizing relay ZCTP may be traced from terminal B over normal contact b and the winding of relay ZCTP, front contact a of signal repeater relay IGYP, and back contact a of transmitter ESQCT to terminal N. it is obvious that the flow of current in this circuit through the relay windin is such as to cause relay ZCTP to operate its contacts to the reverse position, closing reverse contact b. Back contact a of transmitter 18001 is 6 periodically opened, and during this period, the corresponding front contact a is closed. A circuit is then established from terminal B over back contacts an and ar, in series, of relay 2TR, front contacta of transmitter 1259GT, front contact a of relay IGYP, and the winding and reverse contact b of relay ZCTP to terminal N. The flow of current in this circuit is such as to cause the relay to operate its contacts to the left-hand position, closing normal contact b. Back contacts an and ar of relay ZTR assure that a normal code pulse will not be transmitted if the track relay is held energized by foreign current or if the reverse code pulse is unnecessarily prolonged. It is obvious, therefore, that, as contact a of transmitter 180CT alternately closes in its front and back positions, relay ZCTP is alternately energized to operate its contacts to their normal and reverse positions, respectively, so that the relay follows the code rate of the code transmitter.

At times the circuit for relay ZCTP is, completedover back contact a ofrelay IGYP, back contact b of directional stick relay 1S, and front and back contacts a of code transmitter 75CT. Under these conditions, the operation of relay ZCIP is at the, 75 code rate. If back contact a of relay lGYP and front contact b of relay 18 are closed in series, the circuits for relay ZCTP are controlled by contact a of transmitter CT so that the transmitter repeater operates at the 120 code rate. It is obvious from the previously traced track circuits that the operation of contact a of relay 2CTP alternately connects track battery 2TB and track relay 2TR to the rails of the track section, these conections being alternated at the code rate at which the transmitter repeater relay is controlled.

As indicated by the note on the drawing, signal repeater relay IGYP is energized if signal 16 displays a green or yellow aspect to provide a proceed indication for westbound trains. It is to be understood that an indication of the signal position may also be obtained from the position of the home and distant control relays for the signal. -For purposes of simplicity, however, the circuit is shown using only signal repeater relay lGY-P to repeat the signal position, the other arrangements being well known in the art. Directional stick relay 18, as 'indicated in the drawing, is associated also with signal 1G 1 in order to provide for followingmoves in the same direction through the track section. Relay 18 may be controlled in various ways well known in the art, with a specific example of the advance or two-track-circuit pickup arrangement being disclosed in the aforementioned Failor' and Staples application. The control of relays lGYP and 18 is not part of the circuit arrangement embodying my invention and thus these relays have been shown conventionally in order to simplify the drawing and the description.

The reverse code received at the west end of the section by track relay 2TR is decoded by a relay circuit arrangement driven by contacts of the track relay. The distant control relay 2D is energized over an obvious circuit including front contact hr of relay 2TR and the winding of relay 2D. The relay winding is shunted by a resistor-capacitor combination which provides relay 2]) with sufiicient slow release characteristics to permit the relay to retain its front contacts closed it contact br of relay ZTR is only periodically closed in response to code pulses. A somewhat similar circuit for home relay 2H is traced from terminal B over back contact hr and from contact bn of relay 2TR and the winding of relay 2H to terminal N. Relay 2H is likewise snubbed by a resistor-capacitor combination so that it is provided with a slow release period sufficient to retain itsfront contacts closed during coding action of contact 5n. As will appear hereinafter, these snubs mustprovide a suflicient slow release period that the relays will hold front contacts closed even through they are provided with a pulse of energy only during alternate oft-periods of the master code.

of such relays.

' on'eprmorecode following contacts which repeat any code" rate at which'the relay is energized, At leas-tone Th3 circuit for track repeater relaylTP'includes. back contac'tsfbr and brief relay 2TR,. front contacts a, in multiple, of relays 2Dand 2H;backjconta'cta of relay 1S, and the winding ofrelay ZTP. When :front contact aofeither of the other two decoding relays is closed, the winding of relay 2TP-is shunted: by a half-wave rectifier, the snubbiug circuit further including back contact a of relay 1S. When: either or both of contacts .br

and bn-of relay ZTR are following code, relay ZTP is periodically energized and picks up to retain its front contacts" closed; However, the relaygreleases shortly after the interruption of its circuit at front contact a of either of the, other decoding relays, 'the snubbing' circuit also being interrupted under these conditions. Back contact a of relay 1S isincluded in the circuit for relay to assure that; signal 26 displays-a red aspect bebind a; westbonndgtrain occupying the adjacent section to thewest. g 4

The aspect displayed signaliZGis controlled by the position of the decoding relays; Signal 26 is shown, for

circuit including front contacts a and b of relays ZTP and 2H, respectively, andlback contact b of 'r'elayZD. .The circuit for the 'red'lamp, which results'in 'a stop indication,,may be-traced over back contact a of relay ZTP' or over front contacta of relay 2TB. and back contact b of relay 2H. This second ,circuit forlamp R assures. a

andZTP are energizedldue to theoperation of only the "right; armature, of relay 2TR. a a Y 7 j A-tth'e east end,;the master code received by track relayQTR 'isdecbded by 'an arrangement which includes track repeater relays" 180TPand 120TP, distant relay 3D, homerlayBH, an'jdcode. detection relay 3CD., The

circuit arrangement isfsimila'r to that (shown in the previouslymentionedFailor and Staples application, I Track 7 repeater'relays-180TP and 120TP 'arej eachiprovided with 4 I at least [one mechanically tuned. contact arrangement, I 7 this contact .beingt'uned toa c'oderate corresponding to 'the numerical. portion of the. relay referenceeharacter.

As an example, these relays may be asshown and claimed i'n'Let-ters Patent ofthe United States 2,730,592, gran-ted January 10, 19.56 to Andrew. Hufnagel for a CodeFollow ing Relay-fWith Frequency Decoding Contacts. Ref- "eren'ce is made to this patent for a complete description Briefly, the relay may be provided with ot-her transfer.contact is then mechanically tuned to, be responsive only to theselected code rate. V For example, contact 21 of'relay'180TP is responsive, to alternately close .its jtfrontandbac'kcontacts, only when the windingof re1ay 180TP is energized by code pulses at the 180 code rate; Contact def relay .1201? is similarly tuned, but is responsive, alternately closing its front and'back contacts, only .when the relay. is energized by pulsesat the 120 code rate. l-The tuned contacts of these relays are so designated by. a line drawn through the heel of the movable portion of the contact with a numerical designa .tion denoting the code rate. When the relay winding is,

36 display of the stop indication in the event that relays 2D V circuitsicoinpleted', respectively, at frontcontacts a and b oftrack relay 3TR. Distant relay 3D is then energized'by acirouit from terminal B -overdaack contact a of directional 'stick' relay 48, front contact a of relay 18'0TP, and the winding of. relay 3D to terminal N. The

half-Wave rectifier connected in multiple with the relay winding provides a sufiicient slow release period for the relay so that its' front. contacts remain closed as long as the relay winding is periodically energized by the closing of front contact a of relay 180TP at the 180 code rate. Back contact a of directional sticlcrelay 48, which is associated with signal 4G and is'energizedwhen a train passes signal 46 displaying a clear indication in a-man- 'ner similar to that previously discussed for relay 1S, assures that signal 3G willdisplay a stopindication behind an eastbound train in the track section adjacent Ion the east to section'2-3T.I 1 r With back contacts a' of relays 180TP and 120T? closed and also back contact b of 120TP, a circuit is completed, including back contact a of relay 48, to charge capacitor C1 from the local source of direct current energy.. When front contact b of relay 120T? closes during the on-time of the master code, capacitor C1 is discharged over this front contact through the winding of relay 3CD, the circuit being completed from terminal N at the right side of the winding of relay 3CD to terminal N at the left end of resistor R1. Relay 3CD is thus periodically energized at any timethat relay 3TR operates at any code rate and is snubbed by a half-wave rectifier to provide sufiicient slow-release characteristics to retain its front contact closed duringthe coding action..- t v a Home relay SE is' also energized if master code at the 180 code rate is received at this end of the track section. Under this condition, the energizing circuit is completed over front contact b of relay 3D and front "contact'a'ofrelay 3CD to the winding of relay 3H. 'At other times, when pulses at the 120 code rate are being received; the circuit for relay 3H includes-back contact a of relay'AS, back'contact a ofrelay 180TP, front contact a of relay 120TP, which is responsive only to the 120 code rate, and front contact a of relay 3CD. The halfwave rectifier snub is connected innnultiple'with the winding of relay 3H only when front contact a of relay 3CD is closed. Underthis condition, relay 3H'is provided with a sufiicient slow release period to retain its front contacts closed during coding action of :contact a -of'relay 120TP. v and thus relay 120TP l1alts,1the release of'rela y 3CD at If'the coding action of relay 3TR,

the end of its'fslow release period interrupts the s'nu-b circuit and relay 3H releases shortly thereafter.

The control circuits for signal 3G,; which is shown as a color-lightsignal having the lamps G, Y, and R, are similar to those discussed for signal 2G, but do not include 'contact s ofrelay 3 CD. The circuit for lamp G of signal 3G includes front contactsa, series, of relays 3D and 3H.- The yellow lamp Y is energized over back contact a of relay 3Dandfront contact a of relay 3H, Whilean'obvious circuit overback contact a of relay 3H provides energy for lighting lampRb Depending .on whether signal 36 displays a' green, yellow, or red energized by pulsesof energyat any other. code rate,

' I'themechanically tuned contacts remain inoperative'with back contactsclosed. Contact b ef relay 120TP is ofv 1 the non-tuned type and alternately closes its front and 7 when relay120TP is energized at any .coderdte. a

aspect, a clear, approach, or stop indicatiomrespectively, is correspondingly provided.

The reverse cod'e transrnitting'or generating circuits at the east end of the track section includepin addition 'to the transmitter relay 3RC previously defined, 'thefront and back contact track repeater relays3TFP- and-STB-P,

respectively. .Co'nta'cts of stick frelay 4Srand signatre" .pea'ter relay 4GYP also enter intotheoperation of the reverse coding circuits. This latter relay repeats-the position of signal-'46, being :energized ifithis. signal displays a greener. yellow, aspect; As previously discussed in connection with relay lGYP, contacts 'of ,relay 4GYP could be replaced by various contacts-. of the .distantand home relays controlling signal 46, but for simplicity the single repeater has been shown. Relays 3TFP and 3TBP are both of the two-winding, magnetic stick type previously defined. The circuit for the upper winding of relay 3TFP extends from terminal B over front contact of relay 3TR, reverse contact a of relay STEP, and the winding of relay 3TFP to terminal N. A circuit for the lower winding of relay 3T FP includes, in addition to front contact 0 of relay 3TR, normal contact a of relay 3TBP. Similar circuits for relay 3TB? may be traced over reverse and normal contacts a of relay 3TFP and back contact 0 of relay 3TR.

Assuming relay 3TBP to be occupying its normal position, it is apparent that if relay 3TR is energized and closes its front contact 0, the lower winding of relay BTFP is energized with current flowing in the direction to operate its contacts to their reverse position closing, specifically, reverse contact a. If relay 3TR is then deenergized, as during the following off-period of the master code pulses, the circuit completed over back contact c of the track relay and reverse contact a of relay STEP energizes the lower winding of relay 3TBP with a direction of current flow to cause operation of its contacts to their reverse position, closing reverse contact a. During the following master code pulse, the closing of front contact 0 of relay 3TR completes a circuit for energizing the upper winding of relay STFP, with the direction of current flow being such that the relay operates its contacts to their normal position. During the next offperiod of the master code, the upper Winding of relay 3TB? is energized over back contact 0 of the track relay and normal contact a of relay STFP. The direction of current flow is such as to cause relay STBP to operate its contacts to their normal position, closing normal con tact a. The two-relay stepping arrangement has now returned to its initial assumed condition and the closing of front contact (3 of relay STR during the next pulse of master code initiates a repeat cycle of operation. The two track repeater relays thus periodically step between their reverse and normal positions during alternate cycles of the master code. Specifically, relay 3TFP operates, during one on-period of the master code, to close its reverse contacts and, during the next on-period, to close its normal contacts the stepping cycle being completed or assisted by the similar operation of relay 3TBP.

Each time relay 3TR is energized and picks up to close its front contact d, capacitor C2 is charged from terminal B over front contact d of relay 3TR through capacitor C2 and resistor R2 to terminal N. When track relay 3TR releases during an off-period of the master code, and with conditions normal (signals clear) so that relay 4GYP is energized, a first circuit is completed from terminal N through resistor R2, capacitor C2, back contact d of relay 3TR, normal contact b of relay 3TFP, front contact a of relay 4GYP, the winding of relay 3RC, front contact b of relay 4GYP, and normal contact 0 of relay STFP back to terminal N. The charge stored in capacitor C2 discharges through this circuit, the flow of current through the winding of relay 3RC being from left to right so that the left armature is responsive and operates its corresponding contacts. With relay STFP in its reverse position, the circuit includes resistor R2, capacitor C2, back contact d of relay 3TR, reverse contact b of relay 3TFP, front contact b of relay 4GYP, the winding of relay SRC from right to left, front contact a of relay 4GYP, and reverse contact c of relay 3TFP. This time the fiow of current discharging from relay C2 is in the direction to cause the right armature of relay SRC to operate its contacts. relay 4GYP picked up, the stepping operation of relay 3TFP, as controlled by the code following operation of relay 3TR, causes relay 3RC to alternately operate its left and right hand contacts during cit-periods of the master code. From the reverse code track circuits 'previously discussed, it is apparent that this causes the site- It is thus apparent that, with 10 cessive pulses of the reverse code to have alternately opposite polarities.

If relay 4GYP is released, one control circuit for relay 3RC may be traced from terminal N through resistor R2, capacitor C2, back contact d of relay STR, front contact I: of relay 48, back contact a of relay 4GYP, the winding of relay SRC from left to right, back contact b of relay 4GYP, and front contact c of relay 48 to terminal N. Since contacts b and c of relay STFP are bypassed by this circuit, the pulse of current resulting from each discharge or" capacitor C2 is in the direction to cause only the left armature of relay 3RC to operate its contacts. Another circuit arrangement is similar, but includes back contacts b and c of relay 48 instead of the corresponding front contacts. It is apparent that the flow of current through the winding of relay'3RC, under this condition, is reversed so as to be from right to left causing the right armature only to be responsive to operate its contacts. Thus, with relay 4GYP released, but stick relay 4S energized, the reverse code pulses will all be of the positive polarity, while if relay 48 is also released, all of the reverse code pulses will have the negative polarity.

I shall now describe the operation of the signal system for section 2-3T as provided by the circuits embodying my invention. It is believed that, with this operational description, the operation of an A.P.B. signal system for a complete stretch of single track utilizing the circuits of my invention will be obvious to those skilled in the art. In addition, reference is made to the aforementioned Failor and Staples application for further background in the application of these circuits to a complete system.

As shown in Fig. l, the signal system is in the condition which it assumes when the track stretch is unoccupied, that is, there is no train in section 2-3T or in the stretch of single track between the first station east and West of the illustrated track section. Under this condition, signal 1G displays a clear indication and relay 1GYP is energized and picked up. The operation of relay ZCTP is then at the 180 code rate so that the master code pulses flowing in section 2-3T are of this rate. Track relay STR follows each code pulse, picking up. during the pulse on-time and releasing during the ofi-period follow ing. Relays 180T? and 129TP repeat exactly the operation of relay STR, being energized over its front contacts a and b. Contact a of relay 180T? will alternately close its front and back contacts as it is tuned to the 180 code frequency. However, contact a of relay .120TP remains with its back contact closed, as indicated by the solid line position of the movable portion of this contact, since it is tuned to the code frequency and is non-responsive at the code rate. With the track to the east unoccupied, signal 46 is displaying its clear indication so that relay 48 is released. Decoding relays 3D, 3CD, and 3H are thus energized and circuits are completed for energizing the green lamp of signal 3G to provide a clear indication on this signal.

With signal 4G indicating clear, relay 4GYP is energized and its front contacts are closed. Meanwhile, relays 3TFP and 3TBP follow the operation of track relay '3TR. In other words, during successive code pulses when front contact c of relay 3TR closes, relay STFP alternately operates to its reverse and normal positions. Relay 3TBP follows this operation during the corresponding off-period of the pulses, operatingto its reverse and normal positions immediately following the similar operation of relay STFP. With contacts 17 and c of relay 3TFP operating between their reverse and normal positions, relay 3RC is energized during each off-period of the master code by the discharge of capacitor C2, alternately operating its left (n) and right (r) contacts in the manner previously described. With front contacts qn and bn of relay 3RC closed, a pulse of reverse code of positive polarity is transmitted through the rails 'of'tlre "track section from battery 3TB. "When front contacts 1 reverse code pulses.

m1 andbr of relay 3RC are closed during the succeeding off-period of the master code, a pulse, of reverse code of negative polarity is transmitted through the rails of the track section. *Ihepositive and negative pulses of reverse code thus alternate during successive off-periods of 7 the master code.

a ,Track relay 2 TR at'the west end follows this reverse code, its leftland right armatures being alternately responsive to alternately operate the corresponding setsiof relay contacts. With front contacts bn and'br of relay ZTR alternately closing to follow the reverse code, relays 2H and 2D,-respectively,are periodically energized dur- :ing the'oif-periods of the master code and pick up and hold. As previously mentioned, the capacitor-resistor snubs connected in multiple, with each of the relay windings are engineered so as to hold the relay front contacts a 7 closed even when the relays are energized only during alternate pulses of the reverse code, regardless of the code rateiof the master code being transmitted. Since signal 16; is displaying a clear indication, relay 18 is released and the circuit for energizing relay ZTP is periodically completed over back contacts hr and bn of relay ZTR, in series, front contacts a, in multiple, of relays 2D and 2H, and back contact a of relay IS. The half-waverectifier snub-is connected in multiple with the relay winding, as previously mentioned, over front contacts a, in multiple, of the other two decoding relays so that relay ZTP has sufficient'slow release characteristics to hold its front contacts closed during this coding action. With the three decoding relays all energized and picked up, closing their front contacts, the circuit received at signal location lG-t o change to the 75 code rate. In fact, the master code throughout the stretch in any system embodying my'invention will change to ithe 75 code rate. As illus'tratedby the decoding relays associated ,with signal .36, only the code detecting relays CD will be, energized upon the reception of master code of the 75 code rate so thatisignal 16 will provide a" stop indication, that is, will display a red aspect. Relay IGYP is thus deenergized and releases. Since relay 18 is also released, the circuit completed to control relay 7 2CTRover contact. a oflcode transmitter I75CT so that the master code transmitted from this location eastward through section 2-3T is also at the 75 code rate. At

.theeast lend, relay 3TR operates at the corresponding code rate,'repeated.by relays 180TP and 120TP. Contacts aiof theselatter relays are non-responsive to this rate,; holding 'theirback. contacts closed so that relays 3D and 3H release and only relay- 3CD remains ener j gized at this time. V 7

However, the reverse codeitransmitted from the location ofsignal 46 remains of alternate positive and negative pulses, although the rate of occurrence is slower,

corresponding to the 75 code rate of the master code.

. This'eondition results because relay4GYP remains'em erg'ized, .there'being no change in the, indicationdisplayed by" signal 46. At the .west end-track; relay 2TR con- .tinues to operate its. two sets of contacts alternately ,sin'c'ethe two armatures are alternately responsive "to the Relays ZD,.'2H,- and ZTP remainperiodically energized and, hold their front contacts closed. Signal '26 thus continues to display a green aspect. f 1 V i When the train enters section 2 -3T, I the rails are shunted andtrelay ZTR is decnergized sothat all its contacts-release. With contacts bn and br inoperative, relays 2H and 2D release at the end oftheir slow release l 12 periods and interrupt thecirc'uit for relay ZTP which shortlyirelease's. The closing of back contact b of relay 2H- initially energizes; the-red lamp of signal 26 and "eventually back contact 'aof relay ZTP closes to energize the-lamp. Atthe east end, relay 3TRis also shunted and; thus deenergized, releases; This halts the code following, operation of relays 3'IFP, 3TBP, and3RC; Since relay 120TP'is'no longer periodically energized, its contact: b remains released with -the'corresponding back contact closed so that relay 3CD is deenergized and shortly releases. 'By the time the train clears the section immediately adjacent the west end of section 2-'3T, a directional stick relay similar :to relay 45, at the east end 'is picked up to hold signal lG 'at stop, the decoding relays for that section remaining deenergized.

' As the train continues in the eastward direction and passes signal 4G, relay 4Sis energized andpicks up. When the train clears'section;2- -3T, "that is, is entirely east of signal 46,; relay 3TR follows the master code at the 75 code rate being'transmitted'by relay ZCTP from the west end. Operation of relays STBP, 3TFP, and 3RC resumes at this time. 1 However, with'relay 4GYP released and relay 4S picked up, the contacts of relay STFP in the control circuits for relay 3RC are bypassed. As previously described, the circuits established over front contacts b and c of relay' 4S and back contacts a and b of relay 4GYP result in the flow of. current pulses through the winding of relay 3RC, due to the periodic discharge of capacitor C2, being from'left to right so that the normal armature only is responsive to operate the corresponding contacts. The periodic clos: ing of front contacts an and brt of relay 3RC during each oif-period of the master code cause the reverse code transmittedto have, only the'positive polarity.

Thus, at the west end, only the normal armature of relay 2TR is presently r'esponsive to the-reverse code pulses received and only its;associated contacts operate to follow-the code. The operation of contact bn of relay 2TR between its front and back positions energizes relays 2H.and ZTP so that these relays pick up to close their front contacts The. circuit. established over front contacts a' and b of relaysIZTP and 2H, respectively, and

back contact 'b of relay. 2D energizes the yellow' lamp of-signal 2G causing this :''signal .to display an approach indication fora following train. movement. At: this time, thestick-relay associatedfwith signallzG releases permitting. the decoding circuits for the section to. the west tofunctionkand resulting in theidisplay of a clear indicationzby' signal. 16 This operation energizesLrelay lGYP which pickswup,- closing its frontfcontact 1a to complet'efthe' circuit for controlling relay ZCTP over front and iback'contact a of transmitter-1813GT. .The master code pulses being transmittedeastwar'd are thus restored to the'l-80fcode rate. .However, since relay 45 at the east end of the section is energized, its open back contact, .a. interrupts the circuits for all the decoding relays ,and. relays 3D, 3H,'and 3CD.remain deenergized so that signal 3G continuesto'display a red aspect. It is obvious that, as the train continues eastward eventually clearing the .sectionadjacent the east end of section 23T, relay. ,4S.,will release when signal 4G displays an approach indication. The closingof back contacta of re lay'gtS reenergizes the decoding-relayslto permit thedisplayot a proceedindication by signal 36. Relay 4GYP is energizedand picks up .atf-this time, resulting in the restoration of the. alternate positiveand negative pulses of reverse"clode.,, The system shown .for section 2 31 is, at

thistime restored to its normal condition as shown in the drawings. i f b Itis now assumed thata westbounditrain approaches section .,2,-3T. ,In, a mariner similar to that to. be described shortly for signal 2G, theA.P.B. signaling system operatestqplace signal 4ers: itsstop indication, that a is, displayinglared aspectLRelay Z4GYP is thus deenergized and releases. v Sincef relay 4Sis likewise' -rele'ased,

' 13 the circuit for controlling relay 3RC is established over back contacts a and b of relay 4GYP and back contacts 12 and c of relay 43. This bypasses contacts b and c of relay STFP and results in a flow of current through the relay winding from right to left so that only the right armature of relay 3R0 is responsive, operating the associated contacts in accordance with the code following operation of relay 3TR in the manner previously described. The periodic closing of front contacts m; and hr of relay 3RC results in the transmission, through the rails of section 2-3T to the west end, of reverse code pulses having only a negative polarity.

At the west end, thetflow of track current through relay ZTR is from right to left, as wfll be obvious with negative polarit pulses, so that only the right armature of relay ZTR is responsive to the reverse code pulses, operating the associated contacts periodically. Front contact hr of relay ZTR is periodically closed while contact bn remains in its released position closing the corresponding back contact. Under these conditions, relays 2D and ZTP remain energized and relay 21-1 is deenergized and releases at the end of its slow release-period. The closing of back contact 12 of relay 2H establishes a circuit for energizing lamp R of signal 2G and the signal thus displays its red aspect. From the previous description, it will be obvious that the corresponding action cascades through the section immediately to the west of signal 26. If signal 16 is approach lighted, the continued energization of relay 2TP at this time will retain the signal lamps dark so that the approach lighting is effective section by section and not throughout the whole stretch of single track between the stations. If there is no change in the clear indication displayed by signal 16, relay lGYP remains energized and relay Z CTP continues to be controlled by front and back contacts a of transmitter ISlPCT. The master code transmitted eastward through section 2-3T thus remains at the 180 code rate so that signal 3G remains in its clear position.

When the westbound train enters section 2-3T, the track circuits are shunted and relays ZTR and STR release. At the east end, relays 180TP and 120T? are deenergized at this time, their circuits being open at front contacts a and b of track relay 3TR. With relays 136T? and 129T? released so that their back contacts remain continuously closed, decoding relays 3D, 3H, and 3CD are deenergized and release at the end of their slow release periods. The release of relay 3H energizes the red lamp of signal 36 and the signal displays a stop indications t the west end, the non operation of contact br of relay 2TR deenergizes relay 2D and when this relay releases to open its front contact a, relay ZTP is likewise deenergized and quickly releases, it snubbing circuit being open at this time also. The release of relay 2TP causes the selected lamp of signal 16 to be lighted in preparation for the approach of the westbound train. When the train clears the section immediately to the east of signal 46, coding action may resume in that section, but the directional stick relay associated with signal 36, which corresponds in operation to relay 18 at the west end of the section shown, prevents energization of the track repeater relay so that the signal 46 remains with the red lamp energized.

When the estbound train passes signal 1G, the signal is operated to its stop position in a manner similar to that previously described for signal 3G. Relay 18 is also energized at this time and picks up. Thus, when the train clears section 23T, relay ZCTP is controlled by contact a of transmitter 120 CT, the circuit including back contact a of relay lGYP and front contact I) of relay IS. The master code transmitted eastward through section 23T is thus of the 120 code rate and track relay STR operates at a corresponding frequency. Relays 180T? and 129T? are also energized by code pulses at the 120 code rate so that front contact a of relay 129T? is periodically closed since it is tuned to be responsive to this code rate. Contact a of relay 280T? remains closed in its back position. Atthis time then, relays 3H and 3CD are energized. The closing of front contact a of relay 3H completes a circuit over back contact a of relay 3D for energizing lamp Y of signal 38 causing that signal to display a yellow aspect providing an approach indication for a following train.

The release of directional stick relay associated with signal 36 permits signal 4G to operate to its clear position so that relay 4GYP is energized and picks up. The closing of front contacts a and b of relay AGYP returns the control of relay 3RC to contacts b and c of relay STFP. This latter relay, of course, is alternately operating between its normal and reverse positions following the operation of relay 3TR at the 12% code rate. The two armatures of relay 3R0 arealte-rnately responsive to the current flowing through the relay winding and the alternate operation of contact pairs anfihr'z and ar-br of relay 3R0 transmits reverse code pulses of alternate positive and negative polarities. Relay ZTR follows this combination code, alternately operating its normal and reverse armatures and contacts. The al ternate closing of front contacts br and En of relay ZTR energizes relays 2D and 2H. However, although front contacts a of relays 2D and 2H are closed, the open back contact a of realy 1S prevents the energization of relay 2T? and this latter relay remains released. The red lamp of signal 26 continues to be energized over back contact a of relay ZTP and the signal continues to display its stop indication.

When the westbound train clears the section immediately adjacent the west end of section 2-31, signal 16 is controlled to display its approach indication in a manner similar to that previously described for signal 3G. Relay lGYP picks up and changes the operation of relay ZCTP to the code rate, the master code thus returning to this rate immediately. In a manner previously described, the decoding arrangement at the east end of the section operates to cause signal 36 to display a clear indication. Relay 1S releases at this time, permitting the energization of relay ZTP which picks up. With contacts b of relays 2H and 2D already closed, the closing of front contact a of relay ZTP completes the circuit for enerizing lamp G of signal 26 and this signal returns to its clear position displaying a green aspect. The signal system for section 2-3T is thus restored to the condition shown in the drawings.

it is obvious from the above description of the operation of the system for train movements in each direction that, if following moves do occur, similar action will take place for each train movement through section 2-3T. Reference is also made to the aforementioned Failor and Staples application for a more detailed description of such following moves and the complete operation of the A.P.B. signaling system. It is believed to be unnecessary herein to completely describe in detail the action occurring as following moves take place.

Referring now to Fig. 2, I shall describe a second form of reverse code generator and associated apparatus which also embodies my invention. In Fig. 2, only the apparatus at the east end of section 2-3T is shown. However, this apparatus cooperates with the apparatus shown at the west end of the section in Fig. 1. No change in the arrangement at this latter end or the track section is necessary for proper operation of the second form of the reverse code generator. The reverse code generator shown in Fig. 2 is of the general type shown in the aforementioned Failor and Staples application, that is, the three relay, fast application method. As herein shown, it is modified and improved to embody the teachings of my invention to provide three combinations of reverse code pulses to carry active information through the track section. This second form of invention also utilizes some of the additional advantages available due to the physical-features of the code following relay with is I disclosed in the Hufnagel patent; There is also provided a code following front contact repeater ofthe track relay, relay 31?, which repeats directly the coding action of track relay 3TRAQ. Relay 1 3TP,'iS also of the type 'lhavinga mechanically tuned" contact disclosed in the previously mentioned patent. Two reverse code trans- 'mitter' relays are provided to transmit respectively the positive and negative code pulses. iPositive reverse code transmitter relay PRC and negative reverse code'transmitter relay NRC are selected, as will be described shortly, over contacts of a pole changing relay PC which is of the magnetic stick type previously described. However, in this form of the circuit arrangement, this magnetic stick relay has only a single winding. In the decoding arrangement for the master code at this location, the previously described distant relay 3D, home relay 3H, and code detecting relay 3CD are again utilizedi "In addition, there is provided a slow release front contact repeater of track relay 3TRA, the relay 3TFPA. As will be described shortly, this latter relay, in combination with relay 3CD, provides a code detecting arrangement to check: the code followingaction, that is, the alternate closing of front and back'contacts, of both the track relay STRA and the track repeater relay 3TP.

Track relay 3TRA follows the master code pulses received over the track rails from the West end' of the section as transmitted by relay ZCTP. At the beginning of each master code pulse, relay STRA is initiallyenergized through a circuit from one rail of the section over track lead the winding of relay 3TRA in the direction of the arrow, back contact a of relay PRC, backcontact b of relay NRC, and track lead to the other rail of the section. The back contacts of the two reverse code transmitter relays in this circuit assure that the master code pulse is efiective only if no reverse code pulse is being transmitted and the reverse code relays are not inadvertently held energized due to some circuit fault. Track relay 3TRA is held energized by a stick circuit including. the two track leads, the relay winding, and

its own front contact a'. This circuit is effective to hold relay 3TRA energized until the master-code pulse itself terminates, the interruption of the initial circuit by the opening of the back contact of either'reverse code trans 'mitter relay having no effect under this condition.

The closing of front contact b of relay 3IRA completes anobvious circuit for energizingrelay 3T1, this circuit being efiective to periodically energize relay 3TP to also follow the master code pulses received. Each of these relays is provided, as previously mentioned, with a mechanically tuned contact c. Contact c of relay 3TRA is tuned at the 180 code rate so that it follows, alter-' nately closing front and back contacts, only when master code pulses are of this code rate. Contact of relay 3T? is tuned at the 120 code rate and it follows the operation of relay STP only when the master code pulses are of the 120 code rate." Each of these contacts is designated by the conventional symboL'aline drawn through the .heel of the movable portion of the contact. As previously described, these contacts remain'released, closing the corresponding back contact, except when the relay is energized at the coderate to which the contact is tuned. The other two contacts of each relay alternately close the corresponding front and back contacts whenthe relay is energized at any code rate.

The decoding circuit, arrangement herein provided functions, as will be described, in the manner similar to that for the coding arrangement described inconnection with Fig. land provides the same results in keeping with the master code rate received. Relay STFPA is energized by acircuit extending from terminal B over back contact a of directional stick relay '48; front contact a "of relay c a v 71 I V 3TP, and the winding of relay 3TFP A to terminal N. It is obvious that, with back con-tacta of relay. 4S closed,

JreIay-STFPA is periodically energized when'relay 3TP is following code pulses or: any code rate. Relay '3TFPA is'snubbed by a half-Wave re'ctifierconnected in'multiple with the relay winding and is sufiiciently slow release with this arrangement to bridge theopen circuit time of front contact a of relay- 3TP. Relay 4S iside ntical with relay as shown in Fig. 1 and its operation has previously been sufiiciently described. Back contact a of this latter relay interrupts the supply of; energy. from terminal B to the decoding arrangement andthu's assuresthatsignal 30 will display a red aspect, that is,'a stop indication,behind any eastbound train moving through the track section immediately east of section 2-3T. 'Thisfunctionis the same as previously described in connection' with the'arrangement in Fig; '1. I a 1 Code detecting relays 3CD checks the proper code following operation of. contact a er relay 3TP and also the proper operation of: contacts c of this relay and relay STRA. "The circuit fOIJCIJ GIgiZiHg relay '3CD'extends fromterminal B'over backcontacts a of :relays 4S and 3T1, front contact a of relay 3TFPA, the winding of relay 3CD, and back contactsc, in series, of relays 3IP'and 3 TRA to't'erminal' N. 'Relay. 3CD ,is provided with a snubbing circuit including .a resistor-capacitor arrangement which is connectedin'multiplewith the relay winding over front contacts b and a of relay 3TFPA. Relay 3CD has slow release characteristics only when this capacitor-resis'tor snub is connected in multiple with the relay winding. The relay itself isprovided with slow pick-up characteristics, these slow acting characteristics being indicated by a double arrow through each of the relay contacts. The snubbing arrangement is shunted, when relay STFPA is released, over. back contact b of this relay. This shunt assures that the capacitor is discharged during such periods andassists the proper functioning of the slow pick-up characteristics of 'relay3CD; The combination of relays STFPA and 3CD assures correct code following operation of all .relaycontacts involved inthe decoding arrangement, thatris, contact c of relay 3TRA and contacts a and cof relay 3TP. It will be obvious from the remaining decoding circuits described shortly that, unless'relays 3TFPA and 3CD are. bothenergized and picked up, the proper decodinglof the received master code pulses cannot be accomplished; 5'

under these conditions since itis tuned at the 180 code rate and relay 3D is periodically energized-and picksup. This relay is held up by thehalf-wave rectifier snub connected in multiple with the relay winding over front contact b of relay 3CD. If the master code pulses are of the 120 code rate, relay 31-1 is energized rather than relay 3D, the circuit for relay 3H including the relay winding, front contact a of relay 3CD, front contact 0 of relay 3TP, and back contact 0 of relay 3TRA, Relay 3H is periodically energized by the code following operation of contact c of relay 3TP under these conditionssince contact is tuned at the 120 coderate. 'Relay' 3H picks up and is held in this position by the half-wave rectifier snub connected in multiple With the'relay winding over front contact a of relay 3CD. Each of these latter two decod- V in g relays releases quickly after, the release of relay 3 CD when the code reception halts, the snubfor each relay masts 17 it is to be understood that any other type of signal may be used and the circuit arrangement controlling the signal varied in accordance with the type of signal used.

The reverse code transmitter relays are, in effect, front contact repeaters of track repeater relay STP. Each of the reverse code transmitter relays is snubbed by a resistor connected in multiple with the relay winding, although the retardation is not such as to class the relays as slow release. The snub is used only to improve the form and length of the reverse code pulses, that is, the on-period of the reverse code, in order to provide better operation of the system. The circuit for negative reverse code transmitter relay NRC extends from terminal B over front contact b of relay 3TP, reverse contact a of relay PC, and the Winding of relay NRC to terminal N. The circuit for the positive reverse code transmitter relay PRC also includes front contact b of relay 3TP andthen extends over normal contact a of relay PC, front contact a of relay 4GYP in multiple with front contact b of relay 48 to the winding of relay PRC. Relay 4GYP, as previously mentioned as for relay 48, is identical with the similarly designated relay shown in Fig. l. The operation of relay 4GYP has thus been previously described and is not believed necessary to repeat the description here.

It is obvious from the circuits just described that the reverse code transmitter relays are selected over normal and reverse contacts of pole changing relay PC. This latter relay is energized periodically over back contact b of relay STP so that its energization occurs during the ofi-period of the master code and thus alternately with the energization of one of the reverse code transmitter relays. During normal operation of this system, that is, when no train occupies the section or is approaching from either direction, relay PC is energized over a first circuit which is traced from terminal B over back contact b of relay 3TP, front contact I; of relay 4GYP, front contact of relay PRC, normal contact b and the winding of relay PC, back contact 0 of relay NRC, and back contact c of relay 45 to terminal N. It is obvious that this circuit is complete at the beginning of an off-period of the master code following an on-period when relay PRC has been energized, the release of relay PRC, as previously mentioned, being slightly retarded beyond the termination of the pulse of master code. The flow of current through the winding of relay PC in the circuit just described is such as to cause the relay to operate its contacts to the reverse position, closing reverse contact b of the relay. This prepares a second circuit for energizing relay PC which includes back contact b of relay STP, front contact b of relay 4GYP, front contact 0 of relay NRC, and the winding and reverse contact b of'relay PC. The flow of current in this circuit from terminal B to terminal N through the relay winding is in the direction of the arrow and relay PC operates its contacts to their normal position. This second circuit exists at the beg nning of an oif-period of the master code following an on-period when relay NRC was energized and picked up. Since both circuits include front contact b of relay 4GYP, signal 46 must be in its clear position for this alternate operation to occur.

The operation of relay PC thus occurs alternately between its reverse and normal positions and relays PRC and NRC are alternately selected for energization when front contact b of relay 3T1 closes. As will be shortly described, the alternate energization of these two reverse code transmitter relays on successive pulses of master code results in the transmission of alternate positive and negative reverse code pulses through the track section.

If signal 4G displays a red aspect and relay 48 is energized, a circuit for relay PC may extend from terminal B over back contact b of relay 3T1, back contact b of relay dGYP, front contact d of relay 48, back contact 0 of relay NRC, and the winding and reverse contact b of relay PC to terminal N. This circuit exists as an eastbound train passes signal 4G, after relay 48 picks up,

unless relay PC" already occupies its normal position, which it then holds. The flow of current in the last traced circuit through the winding of relay PC is in the direction of the arrow and relay PC operates to its normal posi- 'tion. of the master code, relay PRC is energized over normal contact a of relay PC and front contact b of relay 48. However, when relay 3TP again releases during the next master code off-period to close its back contact b, the circuit for relay PC over its normal contact b is open at front contact b of relay 4GYP while front contact 0 of relay PRC is closed and at back contact a of relay 48 when back contact 0 of relay PRC closes. Since relay PC remains in its normal position, the periodic closing of front contact b of relay STP continues to periodically. energize relay PRC only. As will be shortly described,- the sole operation of relay PRC causes the transmission" of only positive reverse code pulses through the track section.

If relays 4S and 4GYP are both released, as is the condition when a westbound train is approaching the cir-.

this relay operates to its reverse position. During the. next on-time of the master code, relay NRC isenergiZed over reverse contact a of relay PC, as prevlously de-v scribed. During the next ofi-period of the master code, the circuit including reverse contact b of relay PC and front contact 0 of relay NRC is open at front contact b of relay 4GYP. When relayNRC releases, a shunt is placed on the winding of relay PC traced from terminal N over reverse contact b and the Winding of relay PC, back contact 0 of relay NRC, and back contact 0 of relay 45 to terminal N. Relay PC thus remains in its reverse position and relay NRC alone is periodically energized during each on-time of the master code. This results, as will be described shortly, in the transmission of only negative pulses of reverse code.

The periodic operation of relays PRC and NRC, either in combination or singly, results in the transmissionof reverse code pulses through the rails of the section. One circuit may be traced from the positive terminal of track battery 3TB over front contact a of relay PRC, the winding of relay STRA in the direction opposite to the arrow, and track lead to one rail of the section returning from the other rail over track lead back contact a of relay 3TRA, and front contact b of relay PRC to the, negative terminal of track battery 3TB. Thus, when relay PRC is energized and picks up to close its front contacts, a positive polarity pulse of reverse code is transmitted. 'A second circuit is traced from the positive terminal of track battery 3TB over front contact a of relay NRC, back contact a of relay 3TRA, and track lead to one track rail and returning from the other track rail over track lead and back contact b of relay PRC to the negative terminal of the track battery.

The circuit through the winding of relay 3TRA under these conditions is open at back contact b of relay NRC. Thus, when relay NRC is energized and picks up to close its front contacts, a negative polarity pulse of reverse code is transmitted. It is thus obvious that the sole operation of relay PRC or relay NRC results in the transmission of positive or negative reverse code pulses, re spectively. However, the alternate operation of the two reverse code transmitter relays results in the transmission of alternate positive and negative reverse code pulses during the off-times of the'master code.

Referring to Fig. l briefly, the decoding circuits for reverse code at the West end of the track section, which were previouslydescribed, result in the energization of his obvious that during the following on-period and having connections to the rails for transmitting feedback pulses during the intervals between said master code pulses, one feedback pulse of only one polarity for each master code pulse; said feedback transmitting means being further controlled by said trafiic responsive means for establishing the polarity of said feedback pulses to be a first polarity, a second polarity, or alternately said first and said second polarity as said trafizlc responsive means is in its first, second, and third conditions respectively; and feedback decoding means at said first end having connections to the rails and controlled in response to said feedback pulses for operating the first end entering signal in accordance with the polarity of the received feedback pulses.

6. A coded track signal system for a section of single track having an entering signal at each end to govern trafiic in opposite directions entering said section, comprising, a master code transmitting means having connections to the rails at a first end of said section for selectively transmitting through the section rails one of a plurality of code rates, a master code decoding means having connections to the rails at a second end of said stretch and responsive to the reception of said master code pulses for operating the second end entering signal in accordance with the master code rate; a traffic responsive means operable to a first, a second, and a third condition; a transmitter relay means controlled in response to the reception of master code pulses at said second end and by said trafiic responsive means for periodically closing, once in response to each master code pulse, a first set of contacts, a second set of contacts, or said first and said second set alternately according as said trafiic responsive means is in its first condition, its second condition, or its third condition respectively; and a reverse coding means controlled by said first and said second contacts of said transmitter relay means and having connections to the rails at said second end for transmitting feedback pulses through the rails of a first polarity and a second polarity according as said first and said second contacts are closed; and feedback decoding means having connections to the rails at said first end and responsive to the reception of said feedback pulses for operating the first end entering signal in accordance with the polarity of the feedback pulses.

7. A coded track signaling system for a section of track, comprising, means for supplying to the section spaced pulses of master code, a track relay connected to the section and responsive to said master code pulses to operate alternately to a first and a second position, a front contact repeater relay having a first and a second Winding and a first and a second set of contacts respectively closed in response to the energization of said first and said second windings, a back contact repeater relay having a first and a second Winding and a first and a second set of contacts respectively closed in response to the energization of said first and said second windings, circuit means controlled by a first position contact of said track relay and by a first and a second contact of said back repeater relay for energizing said second and said first windings respectively of said front repeater relay, another circuit means controlled by a second position contact of said track relay and by a first and a second contact of said front repeater relay for energizing said first and said second windings respectively of said back repeater relay; a traflic responsive means having a first, a second, and a third condition; a reverse code relay operable to a first, a second, and a third position, means controlled by first position contacts of said reverse code relay for supplying to the section a reverse code pulse of a first polarity, means controlled by second position contacts of said reverse code relay for supplying to said section a reverse code pulse of a second polarity, a first energizing circuit for said reverse code relay including a source of energy, a second position contact of said track relay and first condition contacts of said traflic responsive means to periodically operate said reverse code relay to its first position, a second energizing circuit for said reverse code relay including a source of energy, a second position contact of said track relay and second condition contacts of said trafiic responsive means to periodically operate said reverse code relay to its second position; and a third energizing circuit for said reverse code relay including a source of energy, a second position contact of said track relay, third condition contacts of said traffic responsive means, and first and second contacts of said front repeater relay to periodically operate said reverse code relay alternately to its first and second positions.

8. A coded track signaling system for a section of track, comprising, means for supplying to the section spaced pulses of master code, a track relay connected to the section and responsive to said master code pulses to operate alternately to a first and a second position, a first reverse code relay operable to a first position and normally occupying a second position, a second reverse code relay operable to a first position and normally occupying a second position, a first coding circuit means controlled by first position contacts of said first reverse code relay and a second position contact of said track relay for supplying to said section a reverse code pulse of a first polarity, a second coding circuit means controlled by a first position contact of said second reverse code relay and second position contacts of said track relay and said first reverse code relay for supplying to said section a reverse code pulse' of a second polarity, a pole-changing relay operable to a first and a second position; trafiic responsive means having a first, a second, and a third condition; a first circuit means controlled by said trafiic responsive means in its first condition, by a contact closed when said track relay is in its second position, and by second position contacts of both reverse code relays for operating and holding said pole-changing relay in its first position; a second circuit means controlled by said trafiic responsive means in its second condition, by a contact closed when said track relay occupies its second position, and by second position contacts of both reverse code relays for operating and holding said pole-changing relay to its second position; a third circuit means controlled by said trafiic responsive means in its third condition, by a contact closed when said track relay occupies its second position, and by first and second position contacts of both reverse code relays for alternately operating said pole-' changing relay to its first and its second position following successive master code pulses, an energizing circuit for said first reverse code relay including a contact closed when said track relay occupies its first position, a first position contact of said pole-changing relay, and contacts in multiple closed when said trafiic responsive means is in its first and third conditions to at times periodically operate said first reverse code relay to its first position, and an energizing circuit for said second reverse code relay including a contact closed when said track relay occupies its first position and a second position contact of said pole-changing relay to at times periodically operate said second reverse code relay to its first position.

References Cited in the file of this patent UNITED STATES PATENTS 2,291,579 Judge July 28, 1942 2,360,948 Jerome Oct. 24, 1948 2,555,013 Staples May 29, 1951 2,662,971 Howard Dec. 15, 1953 

